Do not callback if nothing to download from peer.  Resolves issue 61
Do not callback if nothing to download from peer.  Resolves issue 61

git-svn-id: 222f534b05ab2d99128b129c3f2ba69c893481ce@166 a743e126-8abc-4207-e589-8f9b47be99bf

xmt/BitcoinJ